Recent years have seen an increase in the level of regulatory control over the amount and/or types of pollutants and emissions that are released into the environment on an ongoing basis. For instance, in the past decade, regulations of volatile organic compound (VOC) emissions have become stricter, especially with respect to solvent borne coating systems. See e.g., Directive 2004/42/CE of The European Parliament and The Council of The European Union. Moreover, the use of cobalt driers, which are commonly employed in solvent borne systems, has also been restricted. See e.g., Directive 98/98/EC of The Commission of The European Communities. Therefore, in order to satisfy regulations requiring low VOC and cobalt free coatings, waterborne coatings are often looked to as replacements for solvent borne coatings.
Aqueous polymeric acrylic/alkyd hybrid emulsions are an example of such waterborne coatings. These hybrid emulsions advantageously combine low VOC emissions with application properties similar to solvent and water borne alkyds, with the added possibility to formulate without the use of drying agents. The alkyd component of the hybrid emulsion advantageously influences the open time, gloss, flow, haze and substance wetting of the final product; whereas the acrylate component advantageously influences the early blocking resistance, outdoor durability, and reduces yellowing. One challenge in developing these aqueous polymeric acrylic/alkyd hybrid emulsions is in enhancing the compatibility of two basically immiscible systems.
U.S. Patent Application Publication No. 2009/0004394 to Koller et al. (“Koller”) discloses an aqueous polymeric composition comprising an emulsion polymer, which includes, as copolymerized units, carbonyl-functional ethylenically-unsaturated monomers and an autoxidizable material, wherein the polymeric composition is free of any copolymerized carbonyl-functional monomer reactive amine and hydrazine functional groups.
U.S. Pat. No. 6,277,910 B1 discloses a hybrid binder with a dry-solids content of greater than 60%. The blend contains an acrylic dispersion, a surfactant with protective colloids, and an emulsifiable resin. However, one drawback of this hybrid binder is the usage of a cobalt drier, as discussed above. Furthermore, mandatory classification of formulations containing cobalt driers have created significant manufacturing burdens regarding packaging and labeling requirements, at a minimum. See e.g., Dangerous Substances Directive (Directive 67/548/EEC) of The European Union.
International Patent Publication No. WO2011082965A2 discloses a process for producing a water-based alkyd-acrylic hybrid binder with low residual monomer content. The dispersion is obtained by free radical emulsion polymerization of at least one α, β,-unsaturated monomer (M) and optionally at least one further monomer (M1). The addition of the alkyd resin or polyurethane-alkyd emulsion is done after the polymerization of M and M1 under stirring and a temperature between 60-99° C. The high temperature required for incorporation of the alkyd resin has a negative influence on cost saving and carbon footprint.
In accordance with the invention, a new aqueous acrylic polymer dispersion has been developed which shows enhanced compatibility with alkyd resins when formulated into a hybrid acrylic/alkyd binder system. Moreover, even at low concentrations of the more expensive alkyd component, the resultant hybrid binder can be used to produce decorative coatings with the same gloss level and low haze value as pure alkyd resins but with reduced yellowing and improved blocking resistance and without the use of drying agents.